1. Field of the Invention
The present invention relates to plasma display panels, and more particularly, to a pixel architecture that minimizes vertical crosstalk between pixels and increases brightness.
2. Description of the Related Art
Color plasma display panels (PDPs) are well known in the art. Visible light is emitted by phosphors within the panel in response to gas plasma discharges between a pixel's sustain and scan electrode. During an addressing period, sustain electrodes are generally driven with a common potential, while scan electrodes are selected individually. Since the electrodes are on an internal surface of a front plate, the light produced must pass through the electrodes. When transparent electrodes, e.g., indium tin oxide (ITO), are employed, the light simply passes through the electrode. Alternatively, non-transparent apertured electrodes may be devised that allow the light to pass through open apertures in the electrode.
An embodiment of an AC color PDP is disclosed in U.S. Pat. No. 6,118,214 to Marcotte (hereinafter “the '214 patent) in which apertured electrodes are employed on a front plate. More particularly, the AC PDP includes horizontal pairs of apertured sustain electrodes that connect to a sustain bus. Pairs of independent scan apertured electrodes, are interdigitated with the pairs of common sustain electrodes. The apertured electrodes are generally produced using opaque metallic electrode materials such as silver or a film stack of chrome-copper-chrome.
Contrast enhancement bars are horizontally situated in inter-pixel gaps between horizontally adjacent pixels to reduce the light reflectivity of the phosphor. The contrast enhancement bars are opaque and may be conductive or non-conductive. For additional description of contrast enhancement bars, see U.S. Pat. No. 5,998,935 to Marcotte.
During processing, the electrodes are covered by a dielectric layer and a magnesium oxide (MgO) layer. A back plate supports vertical barrier ribs and plural vertical column conductors. The individual column conductors are covered with red, green, or blue phosphors, as the case may be, to enable a full color display to be achieved. The front and rear plates are sealed together and a space there between is filled with a dischargeable gas.
A pixel is a region at an intersection of electrodes. For example, a pixel is defined at an intersection of a sustain electrode and an adjacent scan electrode on the front plate and three back plate column electrodes for red, green, and blue. A sub-pixel, or sub-pixel site, refers to an intersection of individual red, green, and blue column electrodes with the front plate scan/sustain electrode pair.
The PDP operating voltage and power are controlled by the space between adjacent sustain and scan electrodes (hereinafter referred to as a sustain gap), the width of the lines making up the apertured electrodes, and the overall width of electrodes. The sustain and scan electrodes are generally placed to provide a relatively narrow sustain gap and a relatively wide inter-pixel gap.
Alternating sustaining discharges form at the sustain gap, and spread out vertically. The discharge forms a positive column region branching a positively charged anode electrode and a negative glow region drifts across a negatively charged cathode electrode. In the case of apertured electrodes, the line widths and spacing are balanced to maximize light transmission and to maximize discharge voltage uniformity. For example, minimizing the line width to 40-60 microns and spacing the horizontal lines at a distance less than or near the sustain gap dimension (e.g., 100 microns) achieves this balance. In the paired electrode configuration the electrodes on each side of the inter-pixel gap are at the same potential, therefore the inter-pixel gap must be made sufficiently large to prevent plasma discharges from spreading and corrupting an ON or OFF state of an adjacent pixel.
The overall width of the apertured electrodes, the line widths, the line spaces and the dielectric glass thickness over the electrode combine to determine the pixel's discharge capacitance, which controls the discharge power and therefore brightness. For a given discharge power and therefore brightness of each discharge, a number of discharges in a predetermined period of time is chosen to meet an overall brightness requirement for the panel.
The paired front plate electrode configuration of has the advantage of reduced inter-electrode capacitance, which reduces power dissipation resulting from charging and discharging of the inter-electrode capacitance of each sustain pulse. However, there is a possibility of vertical crosstalk resulting from the electrodes on either side of the inter-pixel gap being driven with the same potential. Vertical crosstalk occurs when a discharge at one discharge site spreads into a vertically adjacent discharge site, i.e., for an adjacent pixel, and affects the ON or OFF state of the adjacent pixel. The '214 patent utilizes a relatively large inter-pixel gap to help increase the vertical pixel to pixel isolation. Note that the back plate barrier ribs provide horizontal pixel isolation but no vertical isolation.
The greatest probability of vertical crosstalk occurs during the addressing period when each row is sequentially addressed to place desired sub-pixels in the ON state. In an addressing discharge, the plasma discharge forms between a selected scan electrode and a data electrode and the discharge's positive column spreads along the back plate data electrode to the sustain electrode. With an adjacent electrode at the same potential, the positive column can cross the inter-pixel gap and deplete the charge on an adjacent sub-pixel's sustain electrode. The presence of the contrast enhancement bar has been shown to have little effect on this address crosstalk mechanism.